Two recently published studies suggest that as climate shifts, species around the globe could be alternately growing or shrinking, with results that could radically challenge ecosystems.

In a study by National University of Singapore, researchers pulled together evidence of species around the world getting smaller because of climate change. As Rachel Nuwer (a former Perch blogger) reports in the New York Times Green blog, the change is felt across an ecosystem, starting with plants that—despite extra CO2—struggle to survive on a hotter, dryer planet. With fewer resources available, the smaller you are the easier it will be to nourish yourself and survive. The research also ties nicely to Bergmann’s rule—which posits that big animals thrive in cold places near the Poles while small animals can better take the tropic heat.

While the idea of pygmy polar bears and wee whales seems strange, a separate study presents another sizeable concern in predicting climate change effects. Scientists in California have found that climate change is making birds bigger. The finding flies in the face of expected results and may reflect how birds must increasingly store fat in the event of weather surprises or how climate change has altered plant growth, changing bird diets.

So, what does it all mean? First, the two studies are a great reminder of how complex the effects of climate change are, and though their headlines may sound contradictory, the researchers in each acknowledge that the changes observed are by no means universal across all species.

In fact, the variability is cause for both concern and hope. Variable shrinking may increase the vulnerability of certain species to others (ever smaller prey for slow-to-change predators). However, Gretchen LeBuhn of San Francisco State University, who contributed to the California bird study, explains that the fact that our feathered friends can be so flexible—growing demonstrably within a short time frame—may indicate that they can keep up with our planet’s dramatic changes to their benefit.